Defects in timber

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Defects in timber

• Grade 8

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objectives

• What are defects in timber
• Types of timber defectives
• knots
• Shakes
• Waney edge
• Dry rot

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knots
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Knots
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Knots

• Where a branch has grown out of a tree the grain
  in the trunk becomes very twisted. When this is
  cut through during conversion the result is a
  weaker board and one which is difficult to work.
  Dead knots occur in some softwoods

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knots

• These are distinguished from live knots because
  they show a black line round their circumference
  and they sometimes fall out of the wood leaving a
  hole.

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Shakes

• These are splits along the grain of the wood.
• Heart shakes and star shakes are very similar
  they radiate from the centre or heart (see
  drawing)

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shakes

• Cup or ring shakes follow the annual rings.

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shakes

• End splits are caused by rapid drying from the
  end grain
• Shakes may occur during the felling or as a
  result of faulty seasoning.

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Waney edge

• When the outside of the tree is left as part of a
  board it is called the waney edge. .

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Dry rot
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Dry rot

• This is caused by a fungus growth which lives on
  the wood and thus destroys it. It attacks wood in
  damp, unventilated positions causing it to dry up
  and crumble into dust.

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Fungus Attack
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Fungus Attack

• There are some more or less harmless fungi which
  affect timber. The result is usually to stain the
  wood with grey streaks or patches. This kind of
  fungus spoils a decorative white wood like
  sycamore

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Insect Attack
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Insect Attack
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Insect Attack
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Insect Attack

• There are several vaneties of insect that attack
  wood. One that does serious damage to furniture
  is the common furniture beetle.
• The beetle lays its eggs in cracks and crevices
  of the wood. These hatch into small worms which
  burrow into the wood. They continue to eat their
  way through the wood for up to two years. The
  worms then change into beetles and come out
  leaving a woodworm hole.

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Insect Attack

• It is thus possible for wood to be affected by
  woodworm for a long time before the woodworm
  holes are seen. The beetles are very small-about
  the size of a pin head-and light brown in colour.
  They are active in the summer months and during
  this time they fly about and lay their eggs on
  furniture. They are very fond of the plywood
  backs of cupboards. Although little can be done
  about the worms in the wood, several preparations
  are on the market which poison the beetles as
  they come out and destroy any eggs laid" on the
  surface.

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Dutch Elm Beetle.
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Dutch Elm Beetle.

• This is a fungus which is spread very rapidly
  through elm trees by a small beetle. The fungus
  kills the tree but the timber, though not
  perfect, can be used.

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classwork

• Question
• 1. Show ,by means of sketches what you understand
  by the following star shake, knots, cup shake,
  waney edge
• 2. Write down what you know about the common
  furniture beetle
• 3. Name a fungus which destroys wood particular
  damp unventilated postion